Grease compositions

ABSTRACT

The invention relates to a grease composition having a base oil and a thickener that includes hydrophilic metal oxide particles and one or more esters which contain one or more unsaturated C—C bonds and/or at least one OH group. The hydrophilic metal oxide particles have a BET specific surface area of at least 10 m 2 /g and at least 80% of the hydrophilic metal oxide particles have a particle size in the range of from 5 nm to 900 μm. The amount of the thickener is in the range of from 0.1-40% by weight, based on the total weight of the grease composition. The invention further relates to methods for manufacturing the grease compositions, and the use of the grease compositions for lubricating bearings, gears and couplings.

FIELD OF THE INVENTION

The present invention relates to grease compositions, methods formanufacturing the grease compositions, and the use of the greasecompositions for lubricating bearings, gears and couplings.

BACKGROUND OF THE INVENTION

Grease compositions are widely used for lubricating bearings and otherstructural components. A grease is an essential product to reduce, forexample, wear, friction, running temperatures and energy losses. Greasesare materials which comprise a base oil that is thickened with a metalsoap, and they are usually prepared by reacting a metal hydroxide with afatty acid in the presence of the base oil. Conventional metal soapgreases require an energy intensive grease cooking and milling processin order to achieve proper thermo-mechanical stability. Conventionalmetal soap greases can still be sensitive to poor thermo-mechanicalstability and can require additional treatments. It is known to improvefurther the stability, and thus the lubricating capacity, ofconventional greases by adding solid additives during the thickeningprocess. Examples of such solid additives are, for example, molybdenumdisulfide, graphite, zinc oxide and/or a silica gel. The process ofgrease cooking and milling and additional treatments is relativelyexpensive because it is carried out at an elevated temperature and overa relatively long period of time. Moreover, the greases so prepared arestill unsuitable for a variety of applications, and not all conventionalgreases are suitable for food and beverage processing applications.

Consequently, there is a need for greases which can easily bemanufactured at low costs, which are stable and show highly attractivelubricating properties in terms of low friction performance. Inaddition, there is a need for greases that are biodegradable,environmentally benign and food compatible.

SUMMARY OF THE INVENTION

Object of the present invention is to provide grease compositions whichshow excellent lubricating properties such as grease life performance,corrosion wear and thermo and mechanical stability, and which can easilybe manufactured at low costs and/or are more environmental friendly.

Surprisingly, it has now been found that this can be established whenuse is made of a base oil and a thickener which comprises hydrophilicmetal oxide particles and a particular ester.

Accordingly, the present invention relates to a grease compositioncomprising a base oil and a thickener which comprises hydrophilic metaloxide particles and one or more esters that contain one or moreunsaturated C—C bonds and/or at least one OH group, wherein thehydrophilic metal oxide particles have a BET specific surface area of atleast 10 m2/g and at least 80% of the hydrophilic metal oxide particleshave a particle size in the range of from 5 nm to 900 μm, and whereinthe amount of the thickener is in the range of from 0.1-40% by weight,based on the total weight of the grease composition.

In particular, the present invention thus relates to a greasecomposition comprising a base oil and a thickener which compriseshydrophilic metal oxide particles and one or more esters that containone or more unsaturated C—C bonds, wherein the hydrophilic metal oxideparticles have a BET specific surface area of at least 10 m2/g and atleast 80% of the hydrophilic metal oxide particles have a particle sizein the range of from 5 nm to 900 μm, and wherein the amount of thethickener is in the range of from 0.1-40% by weight, based on the totalweight of the grease composition.

In particular, the present invention also relates to a greasecomposition comprising a base oil and a thickener which compriseshydrophilic metal oxide particles and one or more esters that contain atleast one OH group, wherein the hydrophilic metal oxide particles have aBET specific surface area of at least 10 m2/g and at least 80% of thehydrophilic metal oxide particles have a particle size in the range offrom 5 nm to 900 μm, and wherein the amount of the thickener is in therange of from 0.1-40% by weight, based on the total weight of the greasecomposition.

The present invention in addition relates to a grease compositioncomprising a base oil and a thickener which comprises a hydroxyl groupcontaining metal compound and one or more esters that contain one ormore unsaturated C—C bonds and at least one OH group.

The present invention in addition relates to a grease compositioncomprising a base oil and a thickener which comprises hydrophilic metaloxide particles and one or more esters that contain one or moreunsaturated C—C bonds and at least one OH group, wherein the hydrophilicmetal oxide particles have a BET specific surface area of at least 10m2/g and at least 80% of the hydrophilic metal oxide particles have aparticle size in the range of from 5 nm to 900 μm, and wherein theamount of the thickener is in the range of from 0.1-40% by weight, basedon the total weight of the grease composition.

Suitably, the thickener comprises in addition one or more metal saltssuch as metal sulphonates, metal sulphates, metal phosphates and/ormetal phosphonates.

The grease compositions according to the present invention show anattractive low friction performance, whereas at the same time they caneasily be manufactured at low costs and/or are more environmentalfriendly.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described with reference to the attacheddrawing, showing some non-limiting exemplary embodiments of theinvention, in which:

FIG. 1 is a chart showing the results of the test sample where thevalues of the Stribeck friction coefficient and the entrainment speed[mms-1] measurements obtained on the MTM rig are shown.

DETAILED DESCRIPTION OF THE INVENTION

The thickener to be used in the present grease composition comprises oneor more esters that contain one or more unsaturated C—C bonds and/or atleast one OH group. Preferably, the one or more esters contain one ormore unsaturated C—C bonds and at least one OH group.

Esters are derived from an acid in which one OH group has been replacedby an alkoxy group (—O—). Often esters are derived from a carboxylicacid and an alcohol. Esterification is the chemical reaction of the acidand the alcohol to form the ester and is usually in the presence of acatalyst, a dehydrating agent.

Suitably, the one or more esters are diesters. Suitably, the one or moreesters contain two or more unsaturated C—C bonds. Suitably, the one ormore esters contain at least two OH groups. Suitably, the one or moreesters contain at least two unsaturated C—C bonds and at least one OHgroup. Preferably, the one or more esters contain at least twounsaturated C—C bonds and at least two OH groups. Suitably, the one ormore esters are metal salts. Suitably, the one or more esters compriseglycerol esters, such as for example triglycerol esters.

Suitably, the one or more esters are esterified fatty acids that containone or more unsaturated C—C bonds and/or at least one OH group. It willbe understood that fatty acids are aliphatic monocarboxylic acidsderived from, or contained in esterified form in an animal or vegetablefat, oil or wax. In accordance with the present invention use can bemade of natural and synthetic fatty acids. Suitable fatty acids fromwhich the esterified fatty acids can be made include caprylic acid,pelargonic acid, capric acid, lauric acid, linderic acid, rayristicacid, tsuzuic acid, physetoleic acid, myristoleic acid, pentadecylicacid, palmitic acid, palmitoleic acid, margaric acid, stearic acid,12-hydroxystearic acid, petroselinic acid, oleic acid, elaidic acid,vaccenic acid, linolic acid, linolenic acid, elaeostearic acid,tuberculostearic acid, arachidic acid, eicosadienic acid, eicosatrienicacid, arachidonic acid, behenic acid, lignoceric acid, nervonic acid,hexadocosanic acid, octadocosanic acid and erucic acid.

Suitably, use can be made of a mixture of different esterified fattyacids. Suitable examples of such esterified fatty acids are for examplealkyl oleate esters and alkyl linoleate esters such as methyl oleateester,ethyl oleate ester and ethyl linoleate ester The greasecompositions may also contain a double esterified fatty ester in whichtwo ester groups are present. Suitable examples of such diesters are forinstance dioctylsebacic ester, dioctylsebacate ester and diisooctylsebacate ester. Suitably, the one or more (di)esters contain two or moreunsaturated C—C bonds. In addition, the (di)esters may suitably containat least one OH group. Suitable examples of such esters include suchmethyl-12-hydroxystearate ester, 9-Octadecenoic acid, 12 hydroxy methylester and hydroxy palmitic ester.

The one or more esters to be used in accordance with the presentinvention have a relative polarity which is introduced by means of oneor more unsaturated C—C bonds along the fatty acid chain and/or theintroduction of an OH-group on for example a secondary position in thefatty acid chain. In this way an improved low friction performance couldbe realized.

The esters to be used in accordance with the present invention includebranched and unbranched esters. The esters may contain an amine groupand/or amide group.

Suitably, the thickener comprises in addition one or more metal saltssuch as metal sulphonates, metal sulphates, metal phosphates and/ormetal phosphonates. When the one or more esters are metal salts, theamount of metal (salt(s) is in the range of from 0.1-40% by weight,based on the total weight of the grease composition. When one or moreesterfified fatty acids are metal salts, the amount of metal salt(s) isin the range of from 0.1-40% by weight, based on the total weight of thegrease composition. The metal in the metal salts is preferably an alkalimetal or an alkaline earth metal of Groups 1 and 2 of the PeriodicSystem of Elements, and bismuth. Suitable examples of metals includelithium, potassium, sodium, calcium, aluminium, rubidium, cesium,francium, beryllium, strontium, barium, radium, bismuth and magnesium.In addition it is noted that the metal in the metal salt to be used canbe a semi-metal such as borium. According to a preferred embodimentaccording to the present invention, the metal is an alkaline earthmetal, most preferably calcium.

The present invention preferably provides a grease compositioncomprising a base oil and a thickener which comprises hydrophilic metaloxide particles, one or more metal salts of fatty acids and one or moreesters that contain one or more unsaturated C—C bonds and/or at leastone OH group, preferably esterified fatty acids, as definedhereinbefore, wherein the hydrophilic metal oxide particles have a BETspecific surface area of at least 10 m2/g and at least 80% of thehydrophilic metal oxide particles have a mean particle size of 5 nm to900 μm, and wherein the amount of the thickener is 0.1-40% by weight,based on the total weight of the grease composition.

The metal salts are suitably derived fatty acids selected from the groupconsisting of caprylic acid, pelargonic acid, capric acid, lauric acid,linderic acid, rayristic acid, tsuzuic acid, physetoleic acid,myristoleic acid, pentadecylic acid, palmitic acid, palmitoleic acid,margaric acid, stearic acid, 12-hydroxystearic acid, petroselinic acid,oleic acid, elaidic acid, vaccenic acid, linolic acid, linolenic acid,elaeostearic acid, tuberculostearic acid, arachidic acid, eicosadienicacid, eicosatrienic acid, arachidonic acid, behenic acid, lignocericacid, nervonic acid, hexadocosanic acid, octadocosanic acid and erucicacid.

The one or more metal salts of fatty acids may be metal salts ofdifferent fatty acids. When use is made of two metal salts of differentacids the first metal and the second metal may be the same metal or theymay differ from each other. In another embodiment wherein use is made oftwo metal salts of fatty acids, the fatty acid of the first metal saltand the fatty acid of the second metal salt may be the same fatty acidor they may differ from each other. When two different metal salts offatty acids are used, the at least first and second metals will not bethe same metal when the fatty acid of the first metal salt and the fattyacid of the second metal salt are the same fatty acids, and vice versa.Suitably, the fatty acid of the first metal salt and the fatty acid ofthe second metal salt comprise a different number of carbon atoms.Preferably, the fatty acid of the first metal comprises 2-16 carbonatoms and the fatty acid of the second metal salt comprises 20-24 carbonatoms. Suitably, the fatty acid of the first metal salt is butyric acid,caproic acid, caprylic acid, capric acid, lauric acid, myristic acid orpalmitic acid, preferably caproic acid or caprylic acid. Suitably, thefatty acid of the second metal salt is arachidic acid, behenic acid orlignoceric acid. Such a grease composition is particularly attractive inlow speed applications such as mining and cement applications.Preferably, the thickener includes in addition to the one or more aminesa metal salt of stearic acid, 12-hydroxy stearic acid and/or oleic acid.More preferably, the metal salt is 12-hydroxy stearic acid, preferablyin combination with a metal salt of stearic acid and/or a metal salt ofoleic acid. The thickener may apart from the one or more metal salts offatty acids also contain one or more fatty acids. Preferably, thethickener contains in addition a metal salt of 12-hydroxy stearic acid,stearic acid or oleic acid also 12-stearic acid, stearic acid or oleicacid.

The present invention preferably relates to a grease compositioncomprising a base oil and a thickener which comprises hydrophilic metaloxide particles, one or more esters that contain one or more unsaturatedC—C bonds and/or at least one OH group and one or more fatty acids,wherein the hydrophilic metal oxide particles have a BET specificsurface area of at least 10 m2/g and at least 80% of the hydrophilicmetal oxide particles have a particle size in the range of from 5 nm to900 μm, and wherein the amount of the thickener in the range of from0.1-40% by weight, based on the total weight of the grease composition.

Suitably, the thickener comprises in addition one or more metal saltssuch as metal sulphonates, metal sulphates, metal phosphates and/ormetal phosphonates.

Suitable fatty acids that can be used include caprylic acid, pelargonicacid, capric acid, lauric acid, linderic acid, rayristic acid, tsuzuicacid, physetoleic acid, myristoleic acid, pentadecylic acid, palmiticacid, palmitoleic acid, margaric acid, stearic acid, 12-hydroxystearicacid, petroselinic acid, oleic acid, elaidic acid, vaccenic acid,linolic acid, linolenic acid, elaeostearic acid, tuberculostearic acid,arachidic acid, eicosadienic acid, eicosatrienic acid, arachidonic acid,behenic acid, lignoceric acid, nervonic acid, hexadocosanic acid,octadocosanic acid and erucic acid.

When use is made of two or more different fatty acids the fatty acidssuitably comprise a different number of carbon atoms. Preferably, afirst fatty acid comprises 2-16 carbon atoms and a second fatty acidcomprises 20-24 carbon atoms. Suitably, the first fatty acid is butyricacid, caproic acid, caprylic acid, capric acid, lauric acid, myristicacid or palmitic acid, preferably caproic acid or caprylic acid.Suitably, the second fatty acid is arachidic acid, behenic acid orlignoceric acid. Such a grease composition is particularly attractive inlow speed applications such as mining and cement applications. Inanother attractive embodiment of the present invention, the greasecomposition comprises two different fatty acids, wherein the fatty acidsboth comprise 18 carbon atoms. Suitably, the two fatty acids areselected from stearic acid, oleic acid and 12-hydroxy stearic acid.Preferably, the first fatty acid is 12-hydroxy stearic acid and thesecond fatty acid is stearic acid.

The present invention preferably provides a grease compositioncomprising a base oil and a thickener which comprises hydrophilic metaloxide particles, one or more fatty acids, one or more metal salts offatty acids and one or more esters that contain one or more unsaturatedC—C bonds and/or at least one OH group as defined hereinbefore, whereinthe hydrophilic metal oxide particles have a BET specific surface areaof at least 10 m2/g and at least 80% of the hydrophilic metal oxideparticles have a mean particle size of 5 nm to 900 μm, and wherein theamount of the metal salt(s) is 0.1-40% by weight, based on the totalweight of the grease composition.

The metal salts of fatty acids and fatty acids may be any of the metalsalts of fatty acids and fatty acids as described hereinabove.

The grease compositions according to the present invention arepreferably non-hydroxide grease compositions. Non-hydroxide greasecompositions in accordance with the present invention do not containimpurities such as excess amounts of hydroxide which are normallypresent in greases that are prepared in conventional lime soapmanufacturing processes. The non-hydroxide grease compositions accordingto the present invention are suitably substantially free of freehydroxide ions and/or metal hydroxide. Preferably, the presentnon-hydroxide grease compositions contain less than 0.2% by weight, andmore preferably less than 0.1% by weight of free hydroxide ions and/ormetal hydroxide, based on the total weight of the grease composition.Preferably, the present non-hydroxide grease compositions aresubstantially free of free hydroxide ions and/or metal hydroxide.Preferably, the present grease compositions contain less than 0.2% byweight, and more preferably less than 0.1% by weight of metal hydroxide,based on the total weight of the grease composition. Most preferably,the present non-hydroxide grease compositions are completely free ofmetal hydroxide. It will be understood that OH-groups present on thehydrophilic metal oxide particles or in an fatty acid such as 12-hydroxystearate or the metal salt of such an fatty acid are not to beconsidered free hydroxide ions since they are bonded to silicon atoms orto a carbon atom of the fatty acid. The thickener to be used inaccordance with the present invention is suitably a non-saponifiedthickener.

The grease composition in accordance with the present invention ispreferably a non-hydroxide grease composition wherein the thickenercomprises hydrophilic metal oxide particles, preferably silicon oxideparticles, and one or more esters that contain one or more unsaturatedC—C bonds and/or at least one OH group, wherein the hydrophilic siliconoxide particles have a BET specific surface area of at least 10 m2/g andat least 80% of the hydrophilic silicon oxide particles have a meanparticle size of 5 nm to 900 μm, and wherein the amount of the thickeneris 0.1-40% by weight, based on the total weight of the greasecomposition.

The present invention further provides a grease composition comprising abase oil and a thickener which comprises crystalline hydrophilic siliconoxide particles and one or more esters that contain one or moreunsaturated C—C bonds and/or at least one OH group, wherein thehydrophilic silicon oxide particles have a BET specific surface area ofat least 10 m2/g and at least 80% of the hydrophilic silicon oxideparticles have a mean particle size of 5 nm to 900 μm, and wherein theamount of the thickener is 0.1-40% by weight, based on the total weightof the grease composition.

Examples of esters containing unsaturated C—C bonds include1,2-dilinoleoyl-3-oleoyl-rac-glycerol, glyceryl-trilinoleate, glycerylmonostearate, palmitoleic acid ethyl ester, glyceryl tri-oleate, ethyloleate, methyl oleate, methyl linoleate, methyl linolenoate, oleyloleate, propyl oleate, myristyl oleate, ethyl palmitoleate, ethyllinoleate, oleyl stearate, oleyl myristate, oleyl erucate, methyklerucate, ethyl erucate and linolein.

Examples of esters containing an OH group includeglyceryl-1,2-dioloate-3-palmitate, glyceryl behenate, glyceryl adipate,glyceryl myristate, glyceryl stearate citrate, glyceryl caprylate,glyceryl laurate, glyceryl arachidate, glyceryl palmitate, glycerylhydroxystearate, glyceryl stearate, Methyl 12-hydroxyoctadecanoate andhydroxyl palmitic ester.

Examples of esters containing an OH group and an unsaturated C—C bondinclude glyceryl ricinoleate ester, glyceryl linoleate, glyceryllinolenate, glyceryl palmitoleate, glycerol dioleate, glyceryl erucate,glyceryl oleate, triethanolamine oleate, ethyl ricinoleate, methylricinoleate, O-acetylricinoleic acid methyl ester and ricinolein.

Examples of diesters include diisooctylsebacid acid ester,dioctyladipate acid ester, dioctylsebacate ester, dimethylsebacate esterand diethylsebacate ester.

The present invention further provides a grease composition comprising abase oil and a thickener which comprises crystalline hydrophilictitanium oxide particles and/or hydrophilic aluminium oxide particlesand one or more esters that contain one or more unsaturated C—C bondsand/or at least one OH group, wherein the hydrophilic titanium oxideparticles and/or hydrophilic aluminium oxide particles have a BETspecific surface area of at least 10 m2/g and at least 80% of thehydrophilic titanium oxide particles and/or hydrophilic aluminium oxideparticles have a mean particle size of 5 nm to 900 μm, and wherein theamount of the thickener is 0.1-40% by weight, based on the total weightof the grease composition.

The present invention preferably provides a grease compositioncomprising a base oil and a thickener which comprises hydrophilic metaloxide particles and one or more esters that contains one or moreunsaturated C—C bonds and/or at least one OH group and one or moreamides, wherein the hydrophilic metal oxide particles have a BETspecific surface area of at least 10 m2/g and at least 80% of thehydrophilic metal oxide particles have a mean particle size of 5 nm to900 μm, and wherein the amount of the thickener is 0.1-40% by weight,based on the total weight of the grease composition.

Suitably, the amides to be used in accordance with the present inventioncontain one or more unsaturated C—C bonds and/or at least one OH group.Suitably, the amides to be used in accordance with the present inventioncontain one or more unsaturated C—C bonds and at least one OH group.Suitably, the amides contain two or more unsaturated C—C bonds.Suitably, the amides contain two or more unsaturated C—C bonds and atleast one OH group, preferably at least two OH groups.

Suitable amides that contain one or more unsaturated C—C bonds includeunsaturated amides such as oleamide and linoleamide; diamides such asethylene bis stearamide, hydroxy ethyl ethylene bis oleamide, ethylenebis-12-hydroxystearamide and bishydroxethyl oleylamine; and OH-groupcontaining amides such as hydroxy ethyl ethylene bis oleamide, ethylenebis-12-hydroxystearamide.

Preferably, the unsaturated amides are unsaturated fatty acid amides,more preferably the amides are metal salts of unsaturated fatty acidamides. The amides to be used in accordance with the present inventioninclude branched and unbranched amides. The amides may contain an estergroup.

The present invention preferably relates to a grease compositioncomprising a base oil and a thickener which comprises hydrophilic metaloxide particles, one or more esters that contain one or more unsaturatedC—C bonds and/or at least one OH group and in addition one or moreamines, wherein at least one of the metal salts of fatty acids containstwo or more unsaturated C—C, wherein the hydrophilic metal oxideparticles have a BET specific surface area of at least 10 m2/g and atleast 80% of the hydrophilic metal oxide particles have a mean particlesize of 5 nm to 900 μm, and wherein the amount of the thickener is0.1-40% by weight, based on the total weight of the grease composition.

Suitably, the amines to be used in accordance with the present inventioncontain one or more unsaturated C—C bonds and/or at least one OH group.Suitably, the amines to be used in accordance with the present inventioncontain one or more unsaturated C—C bonds and at least one OH group.Suitably, the amines contain two or more unsaturated C—C bonds.Suitably, the amines contain two or more unsaturated C—C bonds and atleast one OH group, preferably at least two OH groups.

Suitably, the unsaturated amines further include at least one OH-group.Suitable examples of such amines are ethyl hydroxy stearamine andbishydroxyethyl oleylamine, and diamines such as bishydroxyethyloleylamine. The amines to be used in accordance with the presentinvention include branched and unbranched amines.The amines may containan ester group.

Suitably, the one or more amines are fatty acid amines. The one or moreunsaturated amines may suitably in addition contain at least one OHgroup, suitably at least two OH groups. Suitably, the one or more aminescontain two or more unsaturated C—C bonds and at least one OH group.Suitably, the one or more amines are metal salts.

The present invention preferably provides a grease compositioncomprising a base oil and a thickener which comprises crystallinehydrophilic metal oxide particles, one or more esters that contain oneor more unsaturated C—C bonds and/or at least one OH group, one or moremetal salts of fatty acids, one or more fatty acids, one or more amidesand/or one or more amines, wherein the hydrophilic metal oxide particleshave a BET specific surface area of at least 10 m2/g and at least 80% ofthe hydrophilic metal oxide particles have a mean particle size of 5 nmto 900 μm, and wherein the amount of the thickener is 0.1-40% by weight,based on the total weight of the grease composition.

Suitably, the additional one or more metal salts of fatty acids, one ormore fatty acids, one or more amides and/or one or more amines containone or more unsaturated C—C bonds and/or at least one OH group.Preferably, the additional one or more metal salts of fatty acids, oneor more fatty acids, one or more amides and/or one or more aminescontain one or more unsaturated C—C bonds and at least one OH group. Theone or more metal salts of fatty acids, one or more fatty acids, one ormore amides and/or one or more amines may be any of the fatty acids,fatty acids, amides and amines as described hereinabove.

The present invention preferably provides a grease compositioncomprising a base oil and a thickener which comprises hydrophilic metaloxide particles, one or more metal sulphonates, metal sulphates, metalphosphates and/or metal phosphonates, and one or more esters thatcontain one or more unsaturated carbon-carbon bonds and/or at least oneOH group, wherein the hydrophilic metal oxide particles have a BETspecific surface area of at least 10 m2/g and at least 80% of thehydrophilic metal oxide particles have a mean particle size of 5 nm to900 μm, and wherein the amount of the thickener is 0.1-40% by weight,based on the total weight of the grease.

The nature of the base oil to be used in accordance with the presentinvention is not essential. The base oil may be selected from the groupconsisting of mineral base oils and synthetic base oils. Mineral baseoils are derived from crude oils and are either formulated on the basisof aromatic, paraffinic and/or naphthenic base oils. Further, a widerange of synthetic base oils is known and they include esters,poly-alpha-olefins, polysiloxanes and the like.

The base oil to be used in accordance with the present invention maycomprise a base oil blend. Suitably, blends of mineral base oils andsynthetic base oils may be used. The base oil in this invention is onewhich may ordinarily be used as the base oil of a lubricating oil or asthe base oil of a grease, and there are no special restrictions. Asexamples mention may be made of mineral oils, synthetic oils, animal andplant oils, and mixtures thereof. In particular it is possible to use,singly or as mixtures, base oils which belong to Group I, Group II,Group III, Group IV and so on of the API (American Petroleum Institute)base oil categories. Group I base oils include, for example, paraffinicmineral oils obtained by a suitable combination of refining processessuch as solvent refining, hydrorefining, and dewaxing in respect oflubricating oil—o fractions obtained by atmospheric distillation ofcrude oil. Group II base oils include, for example, paraffinic mineraloils obtained by a suitable combination of refining processes such ashydrorefining and dewaxing in respect of lubricating oil fractionsobtained by atmospheric distillation of crude oil. Group II base oilsrefined by hydrorefining methods such as the Gulf Company method have atotal sulphur content of less than 10 ppm and an aromatic content of notmore than 5% and so are suitable for this invention. Group III base oilsand Group 11+ base oils include paraffinic mineral oils manufactured bya high degree of hydrorefining in respect of lubricating oil fractionsobtained by atmospheric distillation of crude oil, base oils refined bythe Isodewax process which dewaxes and substitutes the wax produced bythe dewaxing process with isoparaffins, and base oils refined by theMobil wax isomerisation process. These too are suitable for use in thisinvention. Concrete examples of synthetic oils include polyolefins,polyoxyalkylene glycols such as polyethylene glycol or polypropyleneglycol, esters such as di-2-ethylhexyl sebacate or di-2-ethylhexyladipate, polyol esters such as trimethylolpropane esters orpentaerythritol esters, perfluoroalkyl ethers, silicone oils, polyphenylethers, and so on.

The aforementioned polyolefins include polymers of various olefins orhydrides thereof. Any olefin may be used, and as examples mention may bemade of ethylene, propylene, butene and [alpha]-olefins with five ormore carbons. In the manufacture of polyolefins, one of theaforementioned olefins may be used singly or two or more may be used incombination. Particularly suitable are the polyolefins calledpoly-[alpha]-olefins (PAO). These are base oils of Group IV. GTL (gas toliquid) base oils synthesised by the Fischer-Tropsch method ofconverting natural gas to liquid fuel have a very low sulphur contentand aromatic content compared with mineral oil base oils refined fromcrude oil and have a very high paraffin constituent ratio, and so haveexcellent oxidative stability, and because they also have extremelysmall evaporation losses, they are suitable as base oils for thisinvention. As typical examples of animal and plant oils mention may bemade of castor oil and rape-seed oil. The various aforementioned oilsmay be used singly or in mixtures for the base oil. The aforementionedexamples are listed singly but the invention is not limited thereby.

Preferably, the base oil or the base oil blend to be used in accordancewith the present invention has a kinematic viscosity in the range of 1to 60 000 cSt at a temperature of 40° C. according to DIN 51562/1.Suitable base oils include ISO VG 68, ISO VG 46, ISO VG 32, ISO VG 22,ISO VG 15 and ISO VG 10 oils.

The hydrophilic metal oxide particles to be used in accordance with thepresent invention can be derived from titanium oxide, aluminium oxideand silicon oxide. Preferably, the hydrophilic metal oxide particles arehydrophilic silicon oxide particles. The metal oxide particles may becrystalline metal oxide particles or amorphous metal oxide particles.Preferably, the silicon oxide particles are amorphous silicon oxideparticles. The amorphous silicon oxide may contain various amounts ofwater, implying that it may comprise silicic acid. In this respect it isnoted that silicic acid is a general name for a group of chemicalcompounds, oligomers and polymers consisting of silicon, hydrogen, andoxygen. According to a preferred embodiment of the present invention,the amorphous silicon oxide particles are derived from an amorphoushydrophilic silicon oxide. More preferably, they are derived from anamorphous fumed silicon oxide. Most preferably, the silicon oxideparticles are derived from an amorphous hydrophilic fumed silicon oxide.Fumed silicon oxide is an exceptionally pure form of silicon oxide madefrom silica tetrachloride as a starting material, as is well known inthe art. Suitable sources for the fumed silicon oxide are Aerosil(R)which is commercially available from Evonik Industries (formerly knownas Degussa) or Cap-o-Sil(R) which is commercially available from CabbotCorporation. Preferably, silicon oxide particles have an average size inthe range of from 5-100 microns and have a BET specific surface area inthe range of from 5-100 m2/g.

In accordance with the present invention also mixtures of differenthydrophilic metal oxide particles can be used. For example a mixture ofhydrophilic titanium oxide particles and hydrophilic aluminium oxideparticles can be used.

Suitably, the hydrophilic metal oxide particles have a BET specificsurface area of at least 50 m2/g, more preferably at least 75 m2/g, yeteven more preferably at least 100 m2/g, even yet more preferably atleast 125 m2/g and most preferably at least 150 m2/g Although is itpreferred that the BET specific surface area is as high as possible, itwill usually not be higher than 500 m2/g Methods for determining the BETspecific surface area are well known in the art.

In some embodiments of the present invention, the hydrophilic metaloxide particles have a BET specific surface area of less than 50 m2/g.

According to the present invention at least 80% of the hydrophilic metaloxide particles have a particle size of 5 nm to 900 μm. In someembodiments at least 80% of the hydrophilic metal oxide particles have aparticle size of 5-50 nm, preferably of 5-40 nm, more preferably of10-40 nm and most preferably of 20-40 nm. The total particle sizedistribution of the amorphous silicon oxide particles is preferably inthe range of 1-50 nm.

The grease compositions according to the invention may additionallycomprise other thickening components, e.g. polymers or other fattycompounds that contain one or more OH-groups and/or one or moreunsaturated bonds and/or one or more ester groups and/or one or morearomatic groups. Such thickening components can suitably be present inan amount of less than 3% by weight, preferably less than 2% by weight,based on the total weight of the grease composition.

The grease compositions according to the present invention may compriseother additives to tailor its suitability to a certain use as is wellknown in the art. Such additives include anti-wear agents,anti-corrosion agents, rust inhibitors, friction modifiers,anti-oxidants, VI-improvers and the like as is well known by the personskilled in the art. As suitable examples of such additives sulphonates,sulphates, phosphates and/or phosphonates can be mentioned. Suitablesulphonates include for instance methyl ester sulphonate, sodium methylester sulphonate and calium sulphonate. Suitable sulphates include forexample calcium sulphate, sodium dodecyl sulphate and sodium laurylsulphate. Suitable phosphates include for instance calcium hydrogenphosphate and amine phosphate. Suitable phosphonates include for examplecalcium phosphonate ester and other phosphonate esters.

Other suitable additives include silanes, (alkylated) siloxanes, metalhydroxide silicates, silanols, hydrosilicates, metal bonded siliconcompound such as Mg3(Si2O5)(OH)2. Examples of such additives are forinstance polydimethyl siloxane oil, hexomethyldisiloxane, magnesiumhydrosilicate and other phyllosilicates.

As well as polymethylsilesquioxane, hydrated (metal)silicates, amorphoussilica, and sythetic silica gels, which additives are all used toimprove polymer performance. Such other additives can suitably bepresent in an amount in the range of from 1-40% by weight, preferably2-20% by weight, based on the total weight of the grease composition. Incase the grease composition contains a high amount of such otheradditives, e.g. 20-40% by weight, based on total weight of the greasecomposition, the grease composition will display paste-type properties.Hence, the grease composition in accordance with the present inventionalso includes pastes. The other additives may also include small amounts(less than 3% by weight, preferably less than 2% by weight, based on thetotal weight of the grease composition) of further metal salts of fattyacids, but such metal salts will not substantially contribute to theformation of the grease thickener. In that case the grease compositionwill contain more than four metal salts of different fatty acids. Anumber of grease compositions according to the present invention arehydroxide grease compositions.

The present grease compositions may in addition also contain a smallamount of metal hydroxide. Suitable metal hydroxides include potassiumhydroxide, aluminium hydroxide, calcium hydroxide, lithium hydroxide,sodium hydroxide, magnesium hydroxide barium hydroxide and bismuthhydroxide. Other suitable additives include polypropylene, polyethylene,urea, bentonite, and other greases such as (complex) greases andPTFE/PFPE greases.

A common disadvantage of conventional manufacturing methods is that itrequires a multiple number of hours for blending the various components,gelling and cooling of the grease composition. At a batch scale of about1-5 metric tons, the total cooking (gelling) and cooling can take aboutfour hours or more, whereas grease milling can require two or morehours. Usually, the total manufacturing time takes about eight hours.However, the grease compositions according to the present invention canbe prepared in a very short manufacturing process, wherein blending,gelling and cooling is preferably performed within one hour, morepreferably within half an hour period. The mechanical treatment,preferably grease milling, in accordance with the present invention fora 5 metric ton volume can require about two or two and a half hours. Inaddition, it is observed that conventional grease manufacturingprocesses are carried out at high temperatures, typically in the rangeof from 170-220° C., whereas the present grease composition can suitablybe prepared at a temperature below 90° C., including room temperature.

The present invention also provides methods for preparing the presentgrease compositions. In accordance with the present invention thecomponents of the present grease compositions can be mixed in anypossible order of sequence. Preferably, the hydrophilic metal oxideparticles and the one or more esters that contain one or moreunsaturated C—C bonds and/or at least one OH group are subjected to amechanical treatment, a thermal treatment or to both a mechanicaltreatment and a thermal treatment. Hence, (a) the hydrophilic metaloxide particles or the one or more esters that contain one or moreunsaturated C—C bonds and/or at least one OH group are subjected to amechanical treatment and/or thermal treatment; (b) a mixture of thehydrophilic metal oxide particles and the one or more esters thatcontain one or more unsaturated C—C bonds and/or at least one OH groupis subjected to a mechanical treatment and/or thermal treatment; or (c)a mixture of the base oil, the hydrophilic metal oxide particles and theone or more esters that contain one or more unsaturated C—C bonds and/orat least one OH group is subjected to a mechanical treatment and/orthermal treatment. Preferably, the hydrophilic metal oxide particles,the one or more that contain one or more unsaturated C—C bonds and/or atleast one OH group, or a mixture of these components is before or aftermixing with the other component(s) subjected to a mechanical treatment,a thermal treatment or to both a mechanical treatment and a thermaltreatment.

In accordance with the present invention the entire amount of base oilto be used or parts of the base oil can, for example, be added at one ormore stages of the process. Suitable embodiments of the presentinvention include:

Subjecting a mixture of hydrophilic metal oxide particles and one ormore esters that contain one or more unsaturated C—C bonds and/or atleast one OH group, and optionally any of the hereinbefore described oneor more fatty acids, metal salts of fatty acids, amides and/or amines,to a mechanical and/or thermal treatment, followed by adding to themixture so obtained the base oil and optionally any further additives,and subjecting the grease composition so obtained to a mechanical and/orthermal treatment.

Subjecting a mixture of hydrophilic metal oxide particles and one ormore esters that contain one or more unsaturated C—C bonds and/or atleast one OH group, and optionally any of the hereinbefore described oneor more fatty acids, metal salts of fatty acids, amides and/or amines,to a mechanical and/or thermal treatment, followed by adding to themixture so obtained the remaining part of the base oil and optionallyany further additives, and subjecting the grease composition so obtainedto a mechanical and/or thermal treatment.

Subjecting a mixture of hydrophilic metal oxide particles, the one ormore esters that contain one or more unsaturated C—C bonds and/or atleast one OH group and optionally any of the hereinbefore described oneor more fatty acids, metal salts of fatty acids, amides and/or amines,and the base oil to a mechanical and/or thermal treatment, followed byadding to the mixture so obtained any further additives, and subjectingthe grease composition so obtained to a mechanical and/or thermaltreatment.

Subjecting a mixture of the base oil, the hydrophilic metal oxideparticles and one or more esters that contain one or more unsaturatedC—C bonds and/or at least one OH group, and optionally any of thehereinbefore described one or more fatty acids, metal salts of fattyacids, amides and/or amines, and optionally any further additives, to amechanical and/or thermal treatment.

Subjecting the hydrophilic metal oxide particles to a mechanical and/orthermal treatment of, followed by adding one or more one or more estersthat contain one or more unsaturated C—C bonds and/or at least one OHgroup, and optionally any of the hereinbefore described one or morefatty acids, metal salts of fatty acids, amides and/or amines, to thehydrophilic metal oxide particles so obtained and subjecting the mixtureso obtained subsequently to a mechanical and/or thermal treatment. Thebase oil and optionally any further additives are then added to themechanically and/or thermally treated mixture and the grease compositionso obtained is then subjected to a mechanical and/or thermal treatment.

Subjecting the hydrophilic metal oxide particles to a mechanical and/orthermal treatment, followed by adding the base oil, one or more estersthat contain one or more unsaturated C—C bonds and/or at least one OHgroup, and optionally any of the hereinbefore described one or morefatty acids, metal salts of fatty acids, amides and/or amines, andoptionally any further additives, to the mechanically and/or thermallytreated hydrophilic metal oxide particles, and subjecting the greasecomposition so obtained to a mechanical and/or thermal treatment.

Subjecting one or more esters that contain one or more unsaturated C—Cbonds and/or at least one OH group, and optionally any of thehereinbefore described one or more fatty acids, metal salts of fattyacids, amides and/or amines, to a mechanical and/or thermal treatment,followed by adding the base oil, the hydroxyl group containing metalcompound (preferably hydrophilic metal oxide particles) and optionallyany further additives to the at least one metal salt so obtained, andsubjecting the grease composition so obtained to a mechanical and/orthermal treatment.

Subjecting one or more esters that contain one or more unsaturated C—Cbonds and/or at least one OH group, and optionally any of thehereinbefore described one or more fatty acids, metal salts of fattyacids, amides and/or amines, to a mechanical and/or thermal treatmentof, followed by adding the hydrophilic metal oxide particles to themechanically and/or thermally treated metal salt(s) and subjecting themixture so obtained subsequently to a mechanical and/or thermaltreatment. The base oil and optionally any further additives are thenadded to the mechanically and/or thermally treated mixture and thegrease composition so obtained is then subjected to a mechanical and/orthermal treatment.

As indicated above, the grease composition may comprise any furtheradditives. Such further additives can be added to one or more of thecomponents at any stage of the preparation process of the greasecomposition.

In the process according to the present invention each of the componentsor any mixture of the components can be subjected to a mechanical and/orthermal treatment in any possible order of sequence. For example, allcomponents can be added together after which the mechanical and/orthermal treatment is applied. One of the components (e.g. thehydrophilic metal oxide particles) can first be subjected to amechanical and/or thermal treatment after which one other component(s)(e.g. an ester) or two or more other components (i.e. one or more of theesters and the base oil) can be added to the mechanically and/orthermally treated component, followed by subjecting the greasecomposition so obtained to a mechanical and/or thermal treatment.Alternatively, one of the components (e.g. the hydrophilic metal oxideparticles) can first be subjected to a mechanical and/or thermaltreatment after which one other component (e.g. an ester) can be addedto the mechanically and/or thermally treated component, subjecting themixture so obtained to a further mechanical and/or thermal treatment,followed by adding yet one or more other components (e.g. the base oiland an optionally another ester) to the mechanically and/or thermallytreated mixture so obtained, and subjecting the grease composition thusobtained to a mechanical and/or thermal treatment. According to oneembodiment of the present invention, the hydrophilic metal oxideparticles) are first subjected to a mechanical treatment, a thermaltreatment or to both a mechanical treatment and a thermal treatment.Subsequently, the hydrophilic metal oxide particles so obtained aremixed with the base oil and the one or more esters that contain one ormore unsaturated C—C bonds and/or at least one OH group, and optionallyany of the hereinbefore described one or more fatty acids, metal saltsof fatty acids, amides and/or amines to form a grease composition.

Hence, the present invention also relates to a method for manufacturinga grease composition according to the present invention, which methodcomprises the following sequential steps: (a) subjecting the hydrophilicmetal oxide particles to a mechanical treatment, a thermal treatment orto both a mechanical treatment and a thermal treatment; and (b) mixingthe hydrophilic metal oxide particles so obtained with the base oil andone or more esters that contain one or more unsaturated C—C bonds and/orat least one OH group to form a grease composition.

In case use is made of a plurality of esters, the esters may optionallybe processed together with the hydrophilic metal oxide particles in step(a).

According to another embodiment of the present invention, thehydrophilic metal oxide particles are first mixed with the base oil andthe one or more esters that contain one or more unsaturated C—C bondsand/or at least one OH group, and optionally any of the hereinbeforedescribed one or more fatty acids, metal salts of fatty acids, amidesand/or amines, to form a grease composition, whereafter the greasecomposition so formed is subjected to the mechanical treatment, thethermal treatment or to both the mechanical treatment and the thermaltreatment.

Accordingly, the present invention also relates to a method formanufacturing a grease according to the present invention, which methodcomprises the following sequential steps: (a) mixing the hydrophilicmetal oxide particles with the base oil and one or more esters thatcontain one or more unsaturated C—C bonds and/or at least one OH group,and optionally any of the hereinbefore described one or more fattyacids, metal salts of fatty acids, amides and/or amines, to form agrease composition; and

(b) subjecting the grease composition so formed to a mechanicaltreatment, a thermal treatment or to both a mechanical treatment and athermal treatment. The mechanical treatment is preferably a milling stepwhich can be performed in any suitable milling apparatus, e.g. a highpressure homogeniser, a colloid mill, a three-roller mill (e.g. athree-roller mill) or a worm gear mill. Preferably, the millingapparatus is a worm gear milling apparatus. The milling step can beperformed under inert conditions, i.e. in the absence of air or oxygenand/or in the absence of water (vapour). The thermal treatment ispreferably a heating step. The heating step preferably involves heatingat a temperature in the range of 30-120° C., more preferably 40-110° C.and in particular 45-90° C. In this heating step, the water content ofthe amorphous hydrophilic metal oxide particles is reduced, preferablyto a water content of the hydrophilic metal oxide particles of less than5% by weight, more preferably less than 1% by weight, even morepreferably less than 0.5% by weight, yet even more preferably less than0.25% by weight, based on the total weight of the hydrophilic metaloxide particles. The water content of the hydrophilic metal oxideparticles is usually more than 0.01% by weight, based on the totalweight of the hydrophilic metal oxide particles.

Most preferably, the grease composition is manufactured by optionallysubjecting the hydrophilic metal oxide particles to a thermal treatment,preferably a heating step, to reduce the water content of thehydrophilic metal oxide particles, followed by mixing the hydrophilicmetal oxide particles with the base oil and the one or more esters thatcontain one or more unsaturated C—C bonds and/or at least one OH groupto form a grease composition, whereafter the grease composition soformed is subjected to a mechanical treatment, preferably a millingstep.

As disclosed above, the grease composition according to the presentinvention comprises a base oil, hydrophilic metal oxide particles, morein particular hydrophilic silicon oxide particles, and one or moreesters that contain one or more unsaturated C—C bonds and/or at leastone OH group, wherein the amount of the metal salts(s) is 0.1-40% byweight, based on the total weight of the grease composition.

Suitably, the amount of the hydrophilic metal oxide particles will be0.1-20% by weight, preferably 1-5% by weight, based on the total weightof the hydrophilic metal oxide particles and the esters. The skilledperson will understand how such amounts can be realised starting fromthe respective starting materials.

According to a preferred embodiment of the present invention, the totalamount of the esters, based on the total amount of the hydrophilic metaloxide particles and the esters, is within a range of 0.1-30% by weight,preferably within the range of 0.1-20% by weight, based on the totalamount of the grease composition.

The grease composition according to the present invention can be used inmany applications. However, it is in particular useful for lubricating abearing, preferably a rolling element bearing, e g. a spherical rollerbearing, a taper roller bearing, a cylindrical roller bearing, a needleroller bearing, a ball bearing, and may also be used to lubricate asliding or plain bearing It is furthermore very useful in coupling andgearing applications.

The grease compositions according to the present invention encompassNLGI (National Lubricating Grease Institute) grades ranging from NLGIgrade 000 to NLGI grade 6. Preferably, the grease compositions accordingto the present invention have a dropping point of at least 70° C. up toabout 200° C. according to ASTM D-2265.

When used in low loading gearings, the grease composition has preferablya NLGI grade of 000 to 1. When used in high loading gearings, the greasecomposition has preferably a NLGI grade of 0 to 2. When used inbearings, the grease composition has preferably a NLGI grade of 1 to 4,more preferably a NLGI grade of 2 or 3 and most preferably a NLGI gradeof 2.

Examples

The performance of four grease compositions has been tested ontribological and friction performance on the Ball-on-disc, the MiniTraction Machine, at Imperial College, London UK. In each case the testprocedure consists of four steps, i.e. first a grease working step whichis followed by three consecutive Stribeck step tests. Two grease samplesfrom each of the four grease compositions have undergone the entire testprocedure. These duplications were performed to monitor therepeatability of the test between two different tests carried out in theexact same conditions. The same ball and disc used for each of thegrease samples were cleaned prior to running of the tests and the testrepeat. The tests were run with fresh grease.

The grease working step had the purpose of ensuring an even distributionof the grease and to prepare the same initial condition for each test,by shearing the grease in the same way and for the same time, before thestart of the actual test.

Table 1

TABLE 1 Grease working Stribeck steps step (1st step) (2nd, 3rd, 4thsteps) Load [N] 1 31 Max Hertz pressure [GPa] 0.31 0.96 Temperature [°C.] 60 60 Speed range [mm/s] 5 5-1000 (constant) (in 50 log steps) SRR[%] 0 10 Time [min] 5 6In Table 1, the test operating conditions during the grease working stepand the Stribeck test steps are shown.

In the four test procedure steps, the following operating conditionswere applied:

Step 1—Grease working step: a ball load of 1 N was applied on the discresulting in Hertzian contact pressure of 0.31 GPa, and a constant speedof 5 mm/s, for 5 minutes.

Steps 2-4—The three consecutive Stribeck steps: a ball load of 31 N wasapplied on the disc resulting in a Hertzian contact pressure of 1 GPa,and the speed increased from 5 mms/s to 1000 mms/s at a slide-to-rollratio (SRR) of 10%. This step was repeated three times to monitor therepeatability of the step within the same test, and to analyse thefriction coefficient evolution after each step due to the greasethixotropic character.

A test sample 1 according to the present invention was manufactured froma paraffinic mineral blend base oil of 120 cSt from Scharr, Tunap, and10 wt. % calciumhydroxystearate from Barlocher, 2 wt. % calciumstearatefrom Barlocher, 3 wt. % aerosol from Evonik i.e. hydrophilic siliconoxide primary particles having a BET specific surface area of 175-220m2/g and the primary particle size ranges typically between 7-25 nm, 1.2wt. % triphenylphosphate from M. Volkholz, 2 wt. %

disodiumsebacic acid from M. Volkholz, 0.5 wt. % alkylphosphateaminefrom Ciba, 0.5 wt. % from butylated triphenyl phosphorothionate fromCiba, 0.5 wt. % benzotriazole from Ciba, 2.5 wt. %triphenylphosphorothionate from Ciba, 2 wt. % ditertdodecylpolysulfidefrom Elf Atochem, 5 wt. % dioctylsebasicacid-acid ester from Croda and 5wt. % glyceryl isostearate from Croda. The grease has been composed byadding, mixing and milling in a 3-roller-mill for 30 minutes in total.

For comparison reasons, test sample 1 of the present invention wascompared with three reference greases of the following compositions:

Li-1 comprising of lithium salts as a grease thickener, and having amineral base oil viscosity of 100 mm2/s at 40° C.;

Li-2 comprising lithium salts as a grease thickener, and a mineral baseoil viscosity of 200 mm2/s at 40° C.;

CaSX-1 comprising calcium sulfonate and calcium salts as a greasethickener, and a base oil blend of mineral and synthetic PAO base oil ofa viscosity of 80 mm2/s at 40° C.

In FIG. 1, the results of the test sample 1 and the three referencegrease compositions are compared with each other, whereby the values ofthe Stribeck friction coefficient [−] and the entrainment speed [mms-1]measurements obtained on the MTM rig are shown. The boundary, mixed andfull film lubricating regimes are indicated in the figure over theranges of entrainment speeds.

A test sample 2 according to the present invention has been manufacturedfrom a paraffinic mineral blend base oil of 120 cSt from Scharr, Tunap,and 10 wt. % calciumhydroxystearate from Barlocher, 2 wt. %calciumstearate from Barlocher, 3 wt. % aerosol from Evonik i.e.hydrophilic silicon oxide primary particles having a BET specificsurface area of 175-220 m2/g and the primary particle size rangestypically between 7-25 nm, 1.2 wt. % triphenylphosphate from M.Volkholz, 2 wt. % disodiumsebacic acid from M. Volkholz, 0.5 wt. %alkylphosphateamine from Ciba, 0.5 wt. % from butylated triphenylphosphorothionate from Ciba, 0.5 wt. % benzotriazole from Ciba, 2.5 wt.% triphenylphosphorothionate from Ciba, 2 wt. % ditertdodecylpolysulfidefrom Elf Atochem, 10 wt. % glyceryl isostearate ester from Croda. Thegrease has been composed by adding, mixing and milling in a3-roller-mill for 30 minutes in total.

For comparison reasons, test sample 2 of the present invention wascompared with three reference greases of the following compositions:

Li-1 comprising of lithium salts as a grease thickener, and having amineral base oil viscosity of 100 mm2/s at 40° C.;

Li-2 comprising lithium salts as a grease thickener, and a mineral baseoil viscosity of 200 mm2/s at 40 ° C.;

CaSX-1 comprising calcium sulfonate and calcium salts as a greasethickener, and a base oil blend of mineral and synthetic PAO base oil ofa viscosity of 80 mm2/s at 40° C.

In FIG. 2, the results of the test sample 2 and the three referencegrease compositions are compared with each other, whereby the values ofthe Stribeck friction coefficient [−] and the entrainment speed [mms-1]measurements obtained on the MTM rig are shown. The boundary, mixed andfull film lubricating regimes are indicated in the figure over theranges of entrainment speeds.

A test sample 3 according to the present invention has been manufacturedfrom a paraffinic mineral blend base oil of 120 cSt from Scharr, Tunap,and 10 wt. % calciumhydroxystearate from Barlocher, 2 wt. %calciumstearate from Barlocher, 3 wt. % aerosol from Evonik i.e.hydrophilic silicon oxide primary particles having a BET specificsurface area of 175-220 m2/g and the primary particle size rangestypically between 7-25 nm, 1.2 wt. % triphenylphosphate from M.Volkholz, 2 wt. % disodiumsebacic acid from M. Volkholz, 0.5 wt. %alkylphosphateamine from Ciba, 0.5 wt. % from butylated triphenylphosphorothionate from Ciba, 0.5 wt. % benzotriazole from Ciba, 2.5 wt.% triphenylphosphorothionate from Ciba, 2 wt. % ditertdodecylpolysulfidefrom Elf Atochem, and 10 wt. % dioctylsebasicacid-acid ester from Croda.The grease has been composed by adding, mixing and milling in a3-roller-mill for 30 minutes in total.

For comparison reasons, test sample 3 of the present invention wascompared with three reference greases of the following compositions:

Li-1 comprising of lithium salts as a grease thickener, and having amineral base oil viscosity of 100 mm2/s at 40° C.;

Li-2 comprising lithium salts as a grease thickener, and a mineral baseoil viscosity of 200 mm2/s at 40° C.;

CaSX-1 comprising calcium sulfonate and calcium salts as a greasethickener, and a base oil blend of mineral and synthetic PAO base oil ofa viscosity of 80 mm2/s at 40° C.

In FIG. 3, the results of the test sample 3 and the three referencegrease compositions are compared with each other, whereby the values ofthe Stribeck friction coefficient [−] and the entrainment speed [mms-1]measurements obtained on the MTM rig are shown. The boundary, mixed andfull film lubricating regimes are indicated in the figure over theranges of entrainment speeds.

From FIGS. 1-3, it will be clear that that the test samples 1-3 inaccordance with the present invention constitute an improvement in termsof lubrication and friction when compared with the three referencegrease compositions.

1. A grease composition comprising: a base oil, and a thickener thatprovides hydrophilic metal oxide particles and one or more esters whichcontain one or more unsaturated C—C bonds and/or at least one OH group,wherein the hydrophilic metal oxide particles have a BET specificsurface area of at least 10 m²/g and at least 80% of the hydrophilicmetal oxide particles have a particle size in the range of from 5 nm to900 μm, and wherein the amount of the thickener is in the range of from0.1-40% by weight, based on the total weight of the grease composition.2. The grease composition according to claim 1, wherein the one or moreesters contain one or more unsaturated C—C bonds and at least one OHgroup.
 3. The composition according to claim 1, wherein the one or moreesters contain two or more unsaturated C—C bonds.
 4. The greasecomposition according to claim 1, wherein the one or more esters arediesters.
 5. The grease composition according to claim 1, wherein theone or more esters are metal salts.
 6. The grease composition accordingto claim 1, wherein the one or more esters are esterified fatty acids.7. The grease composition according to claim 1, wherein the thickenerfurther comprises one or more metal salts of fatty acids, one or morefatty acids, one or more amides, and/or one or more amines.
 8. Thegrease composition according to claim 7, wherein the thickener furthercomprises one or more metal salts of fatty acids.
 9. The greasecomposition according to claim 7, wherein the additional one or moremetal salts of fatty acids, one or more fatty acids, one or more amidesand/or one or more amines contain one or more unsaturated C—C bondsand/or at least one OH group.
 10. The grease composition according toclaim 1, further comprising one or more sulphonates, sulphates,phosphates and/or phosphonates.
 11. The composition according to claim1, wherein the metal oxide is silicon oxide.
 12. The compositionaccording to claim 11, wherein the silicon oxide is amorphous fumedsilicon oxide.
 13. The composition according to claim 5, wherein the oneor more metal salts are calcium salts.
 14. A method for manufacturing agrease composition having a base oil, and a thickener that provideshydrophilic metal oxide particles and one or more esters which containone or more unsaturated C—C bonds and/or at least one OH group, whereinthe hydrophilic metal oxide particles have a BET specific surface areaof at least 10 m²/g and at least 80% of the hydrophilic metal oxideparticles have a particle size in the range of from 5 nm to 900 μm, andwherein the amount of the thickener is in the range of from 0.1-40% byweight, based on the total weight of the grease composition, the methodcomprises: mixing the base oil, the hydrophilic metal oxide particlesand the one or more esters that contain one or more unsaturated C—Cbonds and /or at least one OH group in any possible order of sequenceand subjecting before or after mixing the hydroxyl group containingmetal compound, the one or more esters that contain one or moreunsaturated C—C bonds and /or at least one OH group to a mechanicaltreatment, a thermal treatment or to both a mechanical treatment and athermal treatment.
 15. A grease composition having a base oil, and athickener that provides hydrophilic metal oxide particles and one ormore esters which contain one or more unsaturated C—C bonds and/or atleast one OH group, wherein the hydrophilic metal oxide particles have aBET specific surface area of at least 10 m²/g and at least 80% of thehydrophilic metal oxide particles have a particle size in the range offrom 5 nm to 900 μm, and wherein the amount of the thickener is in therange of from 0.1-40% by weight, based on the total weight of the greasecomposition used for lubricating a bearing, a gearing or a coupling.